Seed-borne diseases of plants are, together with soil-borne diseases, ranked among seedling diseases. A seed-borne pathogen causing the seed-borne diseases is often transmitted to the next generation via seeds carrying the pathogen and spread by infecting seedling plants in the next generation.
For example, rice bakanae disease is an agriculturally important seed-borne disease of rice caused by the rice bakanae disease fungus belonging to Fusarium fujikuroi (perfect stage name: Gibberella fujikuroi). The germination of rice seeds (seed paddies) colonized by the rice bakanae disease fungus results in not only that the pathogenic fungus is transmitted to surrounding healthy rice seedlings but also that the infected plants exhibit abnormal spindly growth and yellowing symptoms and afterwards withers. In the withered plants, many conidia of the fungus are formed on the surface of the lower leaf sheath, and the conidia fly apart and adhere to the flower part, pistils, anthers, and anther corpses of surrounding healthy stocks to pollute paddies. The paddies each provide a source of infection in the next year as a seed carrying the fungus (Non Patent Literature 1).
This disease can be effectively controlled by seed disinfection using chemical pesticides such as benomyl and pefurazoate, and has therefore been calmed down in fields for a long time. However, there has been concern that these agents are invalidated since excessive dependence on chemical pesticides hastens the appearance of resistant strains. In addition, the use of a fungicide having a different mechanism such as ipconazole has calmed down the disease. However, the use of chemical pesticides always holds the risk of the appearance of resistant fungi and also has problems, such as environment pollution and remaining in rice. With the current increased concern about environment, there is a need for shifting to environmentally sound and sustainable agriculture, and for example, a physical control method, such as a hot water soaking method, and a biological control method using a microbial pesticide are beginning to be spread as an alternative control technique for chemical pesticides. These methods each take aim at giving a safe feeling to consumers by producing safe agricultural products, reducing an environmental load by plant protection, and controlling pests against which chemical pesticides cannot hardly be used.
Meanwhile, however, the effects of conventional physical control and biological control methods are unstable compared to chemical pesticides and they have the problem of not being capable of sufficiently suppress the occurrence of seed-borne diseases including rice bakanae disease and the problem of resulting in increased labor force associated with treatment. In addition, the microbial pesticide has a problem in terms of cost, and the physical control method has problems, such as complicated treatment and reduced seed germination rate.